Thermostatic switch



H. WEIRICH May l1, 1937.

THERMOSTATIC SWITCH 2 Sheets-Sheet l Filed Feb. 21g 1936 m u m m B FIG. 4I

ATTORNEYS May 11, 1937. H. wElRlcH THERMOSTATIC SWITCH Filed Feb. 2l, 1956 2 Sheets-Sheet 2 FIG. ZI

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ATTORNEYSI Patented May 11, 1937 UNITED STATES PATENT OFFICE 2,080,245 THERMOSTATIC SWITCH Heinrich Weirich, Seoane, Paa Application February 21, 1936, Serial No. 65,034.

lil Claims.- (CL 200-138) This invention relates to thermostatically controlled electric circuit breaking and making cle-- vices and has for its object the provision of a new and improved device of this type.

The thermostatically controlled electric circuit breaking and making devices which have been and now are in general use are so constructed that they operate slowly in the act of opening the circuit. This results in sparking at the contacts with the concomitant, fusing and destruction of the said contacts. Attempts have been made to build thermostatically controlled electric circuit making and breaking devices which will operate so as to cause instantaneous breaking oi the circuit. These, however, are onen to the objection that they are comparatively complicated, that they are expensive to manufacture and pro duce, and, in addition, have certain objectionable structural features. vention to produce an electrical circuit breaking and making thermostat which will operate so as to cause the practically instantaneous breaking of the circuit and yet be comparatively simple in its structure.

Further, thermostatic switches now in general use close slowly once they have opened. Where one of the switch contacts is mounted on a resilient arm (as is sometimes the case) and where the switch is part oi a mechanism subject to vibration (as is often the case) the vibration causes intermittent closing oi the switch during the period that the switch elements are returning from the open position to the full closed position. This results in premature closing of the circuit and in sparking with the resultant dee struction of the switch contacts and possible damage to the element which the switch is sunu posed to protect. lit is an object of this invention to construct a thermostatic switch which will close practically instantaneously.

I attain the foregoing objects by forming a normally closed electric switch of the following ma jor elements:

(d) Switch arms of thermostatically responsive material, each anchored at one oi its ends, free at the other of its ends, and having a contact 'point positioned 4thereon near the free end thereof;

(la) A leaf spring convex for its entire length, :t'ulcrumed at a certain point, free at one of its ends, score-cl at a point intermediate its iulcrurn point and free end and positioned so that said free end overlies and normally contacts the free end oi one oli said switch arms and exerts a pres thermo-static arms so It is an object of this in-` sure thereon in a direction which urges said switch arm towards the other arm.

'in its present preferred embodiment I form my that their free ends nor mally tend to move away from each other to a position where vthe Contact points do not touch each other and I provide a finger so positioned that it holds the lower of said arms in a raised position thereby causing the contact point which it carries to touch the contact point carried by the other anhand so that it prevents the upward motion of said lower arm beyond a certain point. l also 'form the upper of said arms so that it will react to temperature changes more slowly than the lower arm so that it will tend to oppose the motion or said lower arm when both arms are moving in a direction which, if continued, will eventually-result in the opening of the switch.

The inventive concept herein set forth may taire many forms. For the purpose of more clear ly disclosing my invention I have shown in the drawings which form a part hereof and will now describe some of these forms.

in said drawings Figure 1 is a side view ci a iragment of a motor to the conduit box ci which attached my novel thermostatic switch which is also shown in side View. The motor fragment has neen broken away intermediate its ends to permit the showing ci my novel thermostatic switch on as large a scale as possible. A portion oi the switch casing has been bro-ken away to show otherwise hidden parts..

Figure 2 is a diagrammatic View of the motor shown in Figure 1 and the pole winding circuit of said motor with my novel thermostatic switch connected in series in said. circuit.' The thermostatic switch is shown in side view and dissociated from its casing. The dot and dash lines show the position the lower arms it would normally assume if the tongue 35 were not present.

Figure 3 is a top View oi the thermostatic switch shown in Figure with a portion of the spring broken away for the purpose of showing the otherwise hidden upper thermostatic arml and with a portion of the upper thermostatic arm hrolien intermediate its ends for the purpose of nacre clearly showing the otherwise hidden lower thermostatic Figure o is a section taken along the line li-- of 'Figure The full lines show the normal posi# tion of the spring and the thermostatic arms and the clot and lines show the positions assumed by these elements when the motor is overheated.

Figure 5 section taken along the line 5--55 oi 'Figure i.

Figure 6 is a perspective view of the heating element used in my thermostatic switch.

Figure '7 is a perspective view of the spring which constitutes an essential part of my novel switch.

Figure 8 is a section taken along the lines 8 8 of Figure 7. The full lines show the normal position of the spring and the dot and dash lines show the position assumed by the spring when the thermostatic bars are in their respective positions shown by the dot and dash lines in Figure 4.

Figure 9 is a section along the line 9--9 of Figure 8.

Figure 10 is a side view of my novel switch with certain of the base elements broken away and illustrates the rst movement of the thermostatic arms and the spring during that phase of the switch operating cycle which results in the opening of the switch. The full lines show the respective positions of said arms and spring when the switch is closed or at the beginning of the switch operating cycle and the dot and dash lines show the respective positions of these elements just before they pass the snap point of the spring.

Figure l1 is a diagrammatic view of the movement of the spring during the period covered by Figure 10. -The heavy full line denotes the starting point of the spring, the dot and dash line designates the position reached by the spring at the end of the period, and the light full line designates the snap point of the spring.

Figure 12 is a view similar to Figure 10 and illustrates the second and nal movement of the thermostatic arms and of the spring in the switch opening phase of the switch operating circle. A portion of the arm anchoring elements of the switch has been broken away to avoid needless repetition. The full lines show the respective positions of the spring and arms at the beginning of this period and the dot and dash lines show the respective positions of these elements at the end of this period.

Figure 13 is a diagrammatic view of the movement of the spring during the period covered by Figure 12.

The snap point of the spring is denoted by the thin solid line and the position of the spring at the beginning of the phase by the heavy solid line.

ning of this period and the dot and dash lines show the respective positions of these elements at the end of this period.

Figure 15 is a diagrammatic view of the movethe position of the spring at the end of this period. The snap point of the spring is denoted bythe thin solid line, and the position of the Figure 16 is a View similar to Figure 14 and indicates the second movement of the arms and spring during the switch .fr :ng phase of the switch operating cjcle. The full lines show the respective positions of the arms and spring at the beginning of this period and the dot and dash lines denote respective positions of these elements at the end of this period. (It is to be noted that the lower thermostatic arm 3 was stationary during this entire period.)

Figure 17 is a diagrammatic view of the movement of the spring during the period covered by Figure 16. The dot and double dash line shows the position of the spring at the beginning of this period and the double dot and dash line shows the position of the spring at the end of this period. The light solid line indicates the snap point of the spring.

Figure 18 is a view similar to Figure 16 and indicates the third and last movement of the arms and spring during the switch closing phase of the switch operating cycle. The full lines show the respective positions of the arms and spring at the beginning of this period and the dot and dash lines denote respective positions of these elements at the end of this period. (It is to be noted that the lower thermostatic arm 3 was stationary during this entire period.)

Figure 19 is a diagrammatic view of the movement of the spring during the period covered by Figure 18. The double dot and dash line shows the position of the spring at the beginning of this period and the heavy solid line shows the po- 9 sition of the spring at the end of this period. 'I'he light solid line indicates the snap point" of the spring.

Figure 20 is a diagrammatic view showing the movements of the spring during the entire switch operating cycle. The respective lines indicate the same positions as they respectively represented in Figures 11, 13, 15, 17 and 19.

(The arrows in Figures 10 to 20 inclusive indicate the direction of movement of the elements.)

Figure 21 is a schematic view showing the step of rounding the convex spring used in my novel switch. The full lines show the movable elements at the beginning of this step and the dot and vdash lines show these elements at the end of this step.

Figure 22 is a schematic view showing the step oi' scoring the convex spring aforesaid. The full lines show the movable elements at the beginning of this step and the dot elements at the end of this step.

Referring more particularly to the drawings wherein similar reference letters and reference numerals denote similar parts reference letter M denotes a motor to the wall W of the conduit box B of which is attached a tubular casing C which carries my novel thermostatic switch I. ('Ihe motor M and its conduit box B are old in the art and in and of themselves do not constitute a part of my invention. For that reason they have been shown only schematically and will not be described further.)

The casing C consists of the telescoping parts D and E. The part D has depending therefrom the externally threaded tubular portion F which has positioned thereon the two nuts N when the vcasing is not mounted on a motor. The portion F is adapted to extend into the conduit box B through a suitable aperture G formed in the wall W of said conduit box B and combines with said nuts N to serve as the means by which the casing C is attached to said wall W of said conduit box B.

The switch l consists of the upper thermostatic ami 2 the lower tliermostatic arm 3, the spring and dash lines show these 2i. lhese prongs extend 4 and the heating element 5. The elements 2, 3 and 5 are suitably anchored at one of their respective ends in a bearing member 6 and suitably insulated from each other and from the bearing member where necessary. The spring 4 is loosely mounted on the prong 22 which extends through a suitable slot II formed in said spring.

The thermostatic arms 2 and 3 are 'made of material which readily conducts electricity. The upper thermostatic arm 2 is wider than the lower thermostatic arm 3 and therefore responds to an increase or decrease in heat at a slower rate than the lower thermostatic arm. The arm 2 has attached thereto near the free end thereof the contact element 1 and the lower thermostatic arm 3 has attached thereto near the free end thereof the slotted contact element 9. The contact element 9 is so formed and positioned that its slot I receives the tongue or linger 35. The arms 2 and 3 are so formed and positioned that the adjoining faces of the contact elements 1 and 9 would normally be separated were it not for the tongue or finger 35. As is clearly shown by the`r dotted lines in Figures 1 and 2 and by the full lines in Figure 4 the upper face 49 of the tongue 35 contacts the upper shoulder of the slot I0 thereby holding the element 9 in the raised position and causing it to contact the element 1 at all times except when the arms 2 and 3 have been activated by heat to assume their respective dot and dash line positions shown in Figure 4. lf the tongue 35 were not present the arm 3 would fall to the position shown by the dot and dash lines in Figure 2.

As is clearly shown in Figures 'l to 9 inclusive., the spring 4 is convex in cross section, has the slot i I formed therein near one of the ends thereof, and has the two spaced parallel grooves I2 formed therein. The spring 4 is so positioned in the switch I that the grooves I2 fall beyond the outer edge 21 of the bar I8 and that its free end I3 overlies and contacts with and exerts pressure upon the wing 8 which extends from the contact element 1. As a result of this structure the spring 4 continually exerts pressure upon the free end of the arm 2 urging said arm and the contact element 1 which it carries towards the arm 3 and its contact element 9. This force is many times greater when the spring is below its snap point than when it is above the snap point. The foregoing force of the spring is dependent upon the strength of the spring material, the degree of convexity, and the distance of the scored lines and free end oi? the spring from the fulcrum point.

The bearing member Ii consists oi the metallic portion'I4 and the two supporting discs 28 and 29 of insulating material.

The metallic portion I4 consists of the parallel side walls I5, the upper anchoring plate i6, the lower anchoring plate i1, and the bracing bar I8.

Each of the walls i5 has the slot itl formed therein near one of the ends thereoi which results in the formation the two prongs 2li and through suitable apertures formed in the lower anchoring plate I1 and are bent over as shovm Figure 5 whereby they serve means to attach the lower anchoring plate il to the remainder the body portion lil.

The other of the ends or' each ci' the walls i5 terminates in a prong which extends through suitable apertures formed. in the supporting disc il@ and the plate 3@ by said. disc. The prongs are twisted serve to attach the supporting disc te to the walls i3 and the plate 30 to the disc 29. The supportingdisc 29 also serves to support and insulate the plate 34. This plate terminates in the tongue or nger 35 which enters into the slot I0 formed in the contact element 9.

The plate 30 is bent to form the straight arms 3I, the angular arms 32 and the wall 33 parallel to and spaced from the arms 3i. This structure results in a slot 45 between said wall 33 and the plate 34. A suitable insulatingstrlp 46 extends through this slot and insulates thewall 33 from the plate 34.

The inner edge of the upper anchoring plate I6 has the spring bearing prong 22 extending inwardly therefrom and the outer edge of said upper anchoring plate I6 has the disc attaching prong 23 formed thereon. The disc attaching prong 23 extends through a suitable aperture formed in the supporting disc 28 and is bent over whereby it serves as means for attaching the supporting disc 28 to the metallic portion I4. The upper anchoring plate I6, the lower anchoring plate I1, the thermostatic arms 2 and 3, the arm 36 of the heating element 5 and the insulating elements 4D have suitable apertures 24 formed therein through which extend the dowels 25 of non-conducting material. These dowels hold the elements aforesaid against lateral displacement relatively to each other. The arm 31 of the heating element 5 has the slot 38 formed therein which receives the dowels '25 and which also .permits the contraction and expansion o the heating element 5 due to temperature changes.

As is evident from Figures l, 2, 4 and 1d the switch I is normally closed. When closed and positioned in the motor circuit the current ilows y from the wire K leading from H of the motor M tothe plate 33, thence through the arms 31 and 3E or' the heating strip 5, thence through the arms 42 and i3 of the 'll-shaped plate 4I, thence through the thermostatic bar 2 and the contacts 'I and il into the thermostatic bar 3, and thence through the plate 44 and into the Wire L.

Because of its structure the spring 4 exerts its full normal pressure when it is in the position shown by the ull lines in Figure 4. When the free end of the spring is urged upwardly this force increases slowly until the spring reaches the point herein designated as the snap point when said force suddenly and sharply decreases but does not become negative. When the force which urged the free end or the spring upwardly is removed the spring moves from its dot and dash line position towards its full line position in Figure 4 exerting its minimum pressure until the snap point is reached when this pressure suddenly and sharply increases to its below the snap point" value. (In the particular illustration here shown the spring pressure changes from approximately seven ('l) ounces to approximately one (l) ounce when it passes through the snap point going 'up and from one ounce to seven ounces when it passes through the snap point coming down.

The spring l is so designed that its force on its strong side the snap point is suilicient to materially retard the movement oi the iree ends ci the arms 7l ri the switclropening direction. inutil the point is reached when it falls to a su a low point to permit the arm il to complete rapidly its movement to its dot and dash line position in 'Figure a. When the spring passes the snap point in the switch closing direction it is again on the strong side the pole windings ci said point and force is so much greater,

than the physical resistance of the free end of the arm 2 to movement in this direction as to rapidly impei said arm 2 downwardly and cause said aim to complete its switch closing movement rapidly.

The thermostatic arms 2 and 3 are of such material that both the normal and even the overload current oi the motor M which the switch l is designed to protect will readily pass therethrough without heating the same abnormally. The heating strip 5 is of such material that it will readily permit the passage of the normal full load current of the motor which it is designed 'to protect but which wil heat up when an over". ad current of said motor passes therethrough.

Cbviously the normal and overload current will vary with the rating of the motor. Given the rating of a motor and the percent of overload at which the current is to be shut oi any skilled Worker in the art can readily design the elements 2, 5, It and 5 which should be used in the thermostatic switch which should be associated therewith to protect the same.

in .making these calculations the full load current ci any particular motor will be constant. But the value assumed for the permissible overload and the point at which the element 5 will begin to heat in order that it may cause the elements 2 and 3 to function to break the circuit by the time the overload current is actually reached will vary. For this reason the elements 2, 3 and 5 designed by diierent workers will vary with certain limits.

For the purpose of illustration only and not for the purpose of limitation the following example is here given.

Let it be assumed that it is desired to design one of my novel thermostatic switches for use4 with a 229 volt-it horse-power-GO cycle-1750 R. P. N12-single phase motor. The normal full load current is 2 amperes.

Let it be further assumed that the underwriters permit an overload of 40% of the normal current. Then current at which the thermostat switch should function to break the current=2 amperes plus 40%X2 amperes=2-8 amperes.

Let it be iurther assumed that for the elements 2 and 3 to function to break the circuit when the current in the motor windings reaches 2.8 amperes it is necessary that the element 5 begin to heat up at 35% of the overload current. Then this current will be 2 amperes plus 35% X2 amperes=2-7 amperes.

The element 5 must therefore be so formed that it will permit a current of less than 2.7 amperes to pass therethrough without heating appreciably but which will heat up if a current or 2.7 amperes or greater passes therethrough. The elements 2 and 3 must be so formed that they will permit a current of 2.8 amperes and even greater to pass therethrough without heating appreciably.

I have found that if desired the heating strip 5 may be omitted and the arms 2 and 3 may be made to serve both as thermostatic arms and as heating units for the same. When the thermostatic arms 2 and 3 also serve as heating elements my novel switch consists of all of the elements shown in the drawings with the exception of the heating strip 5. In such cases either the arm 2 or 3 or both are so designed as to permit the normal motor current to pass therethrough without heating appreciably but which will become heated when a motor overload current passes therethrough. I have found this structure to be particularly feasible in thermostatlc switches which are to be used with motors of higher rating beginning with 110 volt- V2 horse-power-GO cycle- 1750 R. P. M-singlc phase motors.

Although the manner in which my novel switch functions is believed to be obvious from the foregoing diclosure, yet to obviate the possibility of any misunderstanding the following detailed description is here given:

Let it be assumed that an overload current is passing through the circuit in which my novel switch l is positioned. As a result the heating strip 5 will heat up and in turn cause the thermostatic arms 2 and 3 to be hot. This in turn will automatically result in the following cycle ot movements the iirst phase of which culminates in the opening of the switch and the second phase of which culminates in the closing of the switch.

of the switch (l) The thermostatic arms 2 and 3 and the spring 4 move in the following manner from their respective full line positions in Figure l0 to their respective dot and dash line positions in said igure: Both arms rise slowly against the pressure of the convex spring with the arm 2 moving more slowly than the arm 3 since it responds to temperature changes more slowly than the arm 3. This continues until the snap point" or dead center of the spring is reached. The total angular movement of the arms 2 and 3 and the spring l during this period is schematically designated by the angle a in Figures 1l and 20. (During this period the pressure at the contacting faces of the contact points becomes continually greater due to the pressure of the spring and the pressure resulting from the difference in the relative speed of movement of the two arms. Further due to the pressure of the-spring the arms 2 and 3 move a smaller distance than they would have if their movement had been unhampered. Further, it is to be noted that the finger 35 is so positioned that the face Il of the slot l0 ls only a slight distance from the lower face 50 of the finger 35.)

(2) As soon as the spring reaches its "dead center or snap point said spring and the arms 2 and 3 suddenly rise from their respective full line positions to their respective dot and dash line positions shown in Figure 12: 'I'he spring 4 and arm 2 move through the comparatively large angular distance'schematically designated by the angle b in Figures 13 and 20. The arm 3 however moves only a comparatively short distance to the point where the floor 48 of the slot I0 contacts the lower face 50 of the finger 35 at which point its progress is suddenly arrested. (During this period the contacting faces of the Contact points 'I and 9 carried by the arms 2 and 3 respectively suddenly separate and remain separated thus suddenly opening the switch.)

B. In the cycle which culminates in the closing of the switch (l) The thermostatic arm 3 moves downwardly at a much more rapid rate than the thermostatic arm 2 since it responds to temperature changes more rapidly than the aim 2. Therefore while the arm 3 is moving from the position shown by the full lines in Figure 14 to its dot and dash line position in said iigure the arm 2 and spring 4 move through a `muchvshorter distance from their respective full line positions to their respective dot and dash line positions in said ligure. The angular distance travelled during this period by the spring 4 which is the same as the arm 2 which it contacts is schematioally shown by the angle c in Figure 15. (The arm 3 reaches its switch closed position in this period, that is, the roof 41 of the slot I0 comes into contact with the upper surface 49 of the tongue 35 and is held against further downward movement by said tongue.)

(2) The arm 2 and the spring which follows it now continue to move downwardly through the angular distance schematically designated by the angle d in Figures 17 and 20 until the snap point or dead center line of the spring is reached. (During this period the arm 2 and spring 4 move from their respective full line positions in Figure 16 to their respective dot and dash line positions in said gure. The arm 3 having reached its switch closed position in the first period of this phase remains stationary during this entire period.)

(3) The moment the spring 4 reaches its snap point it suddenly increases the amount of its pressure in a downward direction and tends to move rapidly from its full line position in Figure 18 to its dot and dash lineposition in said ligure. The spring is so designed that the force which it now exerts is' suiiicient to overcome the physical resistance of the free end of the arm 2 to downward motion at this point and actuate said arm rapidly from its full line position shown in Figure 18 toits dot and dash line position in said figure causing the lower face of the contact l to impact upon the upper face of the contact 9 thus suddenly closing the switch. (The angular movement of the spring 4 and the arm 2 which it actuates during this period is schematically shown by the angle e in Figures 19 and 20. The arm 3 having reached its switch closed position inthe rst period of this phase is stationary during this entire period.)

Further cooling of the arms 2 and 3 merely results in a greater pressure between the contacting surfaces of the contact points 'l and 9.

The foregoing cycle of movements takes place in exactly the same way in that modification of my switch in which the heating element is eliminated and the arms 2 and 3 are so formed that they will function as heating elements as well as the'rmostatic arms.

Although the manner of making the spring 4 is believed to be obvious yet with a view to obviating any possibility of a misunderstanding the following detailed description is here given.

The springs are first cut in proper lengths and each length is then placed in the die as schematically shown by the full lines in Figure 2l. The male member of the die then forces the spring to the dot and dash line position in Figure 21 thereby imparting convexity to the spring. Thereafter the spring is placed upon the female member of the die shown in Figure 22 with the curve upward as shown in Figure 22. The male member of the die then pushes the spring downwardly to the dot and dash line position shown in Figure 22." This forms the lines l2 in said spring completing the same.

The above disclosure is toA be understood as being by the way of illustration only and not by the way of limitation since many changes maybe made in the disclosure here shown without departing from the spirit of my invention which in its broadest aspect consists in forming an electric switch of the following elements:

(1) Switch arms of thermostatically responsive material, each anchored at one of its ends, free at the other of its ends, and having a contact joint positioned thereon near the free end thereof; and

(2) A leaf spring convex for its entire length, fulcrumed at a certain point, free at one of its ends, scored at a point intermediate its fulcrum point and free end and positioned so that said free end, or finger carried thereby, overlies and normally is in contact with the free end of one oi said arms, or a finger carried thereby.

In another of its aspects my invention consists in forming the thermostatic arms aforesaid so that in the absence of some restraining member the free ends would normally tend to move away from each other to a position where the contact points are out of contact with each other and in providing means which will contact with at least one of said arms and cause it to remain in contact `with the other under normal operating conditions.

In another of its aspects my invention consists in so forming the thermostatic arms aforesaid that one will react to temperature changes more slowly than the other and in so positioning said slower reacting arm that it will tend to oppose the motion of the faster reacting arm when both said arms are moving in the direction which, if continued, will eventually result in the opening of the switch.

In another of its aspects my invention consists in providing means with one of the to prevent its motion beyond a certain point when the arms are moving to either open or close the switch.

-In another of its aspects my invention consists in so forming the thermostatic arms aforesaid that they will permit the normal motor current to pass but will heat up when an overload current passes therethrough.

Having described my invention what I claim as new and useful is:

1. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material each anchored at one of its ends and free at the other of its ends carried by said base member; and a leaf spring convex for its entire length, fulcrumed at a certain point, and free at one of its ends, carried by said base member and pos'tioned so that said free end of said spring exerts a pressure upon the free end of one of said arms urging it to contact the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in the switch opening direction until a certain point is reached when the force in said spring opposing said arm -movement is suddenly diminished to permit a quick separation of the free ends of said arms.

2. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material each anchored at one of its ends and free at the other of its ends carried by said base member; a contact element positioned on each of said arms near the free end thereof; and a leaf spring convex for its entire length, fulcrumed at a certain point and free at one of its ends carried by said base member and positioned so that said free end of said spring exerts which will cooperate l thermostatic points aforesaid a pressure upon the free end of one of said arms it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in the switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of said Contact elements.

3. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member, one of said arms being formed so as to react to temperature changes at a slower rate than the other and each of said arms being anchored at one of its ends and free at the other of its ends; and `a leaf spring convex for its entire length, fulcrumed at a certain point, free at one of its ends, scored at a point intermediate its fulcrum point and free end carried by said base member and positioned so that said free end of said spring exerts a pressure upon the free end of the slower reacting of said arms urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of the free ends of said arms thereby opening said switch, said spring also contacting, urging and following said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring in the switch closing direction is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position.

4. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material each anchored at one of its ends and free at the other of its ends carried by said base member, one of said arms being formed so as to react to temperature changes at a slower rate than the other; a contact element positioned on each of said arms near the free end thereof; an electrical conducting and resistance element carried by said base member and positioned intermediate said arms, said conducting and resistance element being so formed as to readily conduct the normal current of the circuit in which the switch is to be used but to heat up if an overload current goes through said circuit; and a leaf spring convex for its entire length, fulcrumed at a certain point, free at one of its ends, scored at a point intermediate said fulcrum and free end carried by said base member and positioned so that said free end of said spring normally exerts a pressure upon the free end of one of said arms urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of said contact elements thereby suddenly opening said switch, said spring also contacting and following said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring suddenly is increased to a point where it overcomes the resistance of said arm and forcessaid arm to move quickly to its switch closing position thereby suddenly closing said switch.

5. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material each anchored at one of its ends, free at the other of its ends, and so formed that in the absence of a restraining force said free ends would normally tend to move away from each other; means positioned on said base member for preventing the motion of one of said arms beyond a certain point in the switch opening direction and for holding said arm in a raised position when said switch is closed; and a leaf spring convex for its entire length, fulcrumed at one of its ends, scored at a point intermediate said fulcrum point and free end carried by said base member and positioned so that said free end of said spring normally exerts a pressure upon the free end of the slower reacting of said arms urging it to contact the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of the free ends of said arms thereby opening said switch, said spring also contacting and following said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring in the switch closing direction is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position. l

6. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member each of said arms being anchored at one of its ends', free at the other of its ends, and so formed that in the absence of a restraining force at least one of said free ends would normally tend to move away from the other; a contact element positioned on one of said arms near the free end thereof; a slotted contact element positioned on the other of said arms near the free end thereof for cooperative contact with the first of said contact elements; a finger carried by said base member and positioned so as to extend into the slot of said slotted contact element for alternately contacting the roof of said slot to limit the motion of said contact element in one direction and the floor of e said slot to limit the motion of said contact element in the opposite direction; and a leaf spring convex for its entire length, fulcrumed at a certain point, free at one of its ends, scored at a point intermediate said fulcrum and free end carried by said base member and positioned so that said free end of said spring normally exerts a pressure upon the free end of the arm carrying the first of said contact elements urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly vdiminished to permit a quick separation of said contact elements thereby suddenly opening said switch, said spring also following and contacting the arm carrying the first of said contact elements in the switch closing direction until a. certain point ls reached when the force in said spring is suddenly increased to 'a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position thereby suddenly closing said switch.

7. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member one of said arms being formed so as to react to temperature changes at a slower rate than the other and each of said arms being anchored at one of its ends, free at the other of its ends, and so formed that in the absence of a restraining force the free end of at least one of said arms would normally tend to move away from the free end of the other; a contact element positioned on the slower reacting of said arms near the -free end thereof; a slotted contact element positioned on the other of said arms near the free end thereof for cooperative contact with the first of said contact elements; a nger carried by said base member and positioned so as to extend into the slot of said slotted contact element for alternately contacting the roof and floor of said slot todimit the motion of said contact element in the switch closing and opening directions; and va leaf spring convex for its entire length, fulcrumed at a certain point,

f of said slot to free at one of its ends, scored at a point intermediate said fulcrum and free end and positioned so that said free end of said spring normally exerts a pressure upon the free end of said slower reacting arm urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick 'separation of said contact elements thereby suddenly opening said switch, said spring also following, urging and contacting said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position thereby suddenly closing the said switch.

8. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member one of said arms being formed so as to react to temperature changes at a slower rate than the other and each of said arms being anchored at one of its ends, free at the other oi its ends, and so formed that in the absence of a restraining force the free end of at least one oi' said arms would normally tend to move away from the freeend of the other; a contact element positioned on the slower reacting of said arms near the free end thereof; a slotted contact element positioned on the other of said arms near the free end thereof for cooperative contact with the rst of said contact elements; a finger carried by said base member and positioned so as to extend into the slot of said slotted contact element for alternately contacting the roof of said slot to limit the downward motion of said contact element and the floor limit the upward motion of said contact element; a fulcrum carried by said base member; and a leaf spring convex for its entire length, free at one of its ends, grooved at a point intermediate its ends carried by said base member and positioned so that said grooves fall between said fulcrurn and the free end of the spring and so that said free end of said spring normally exerts a pressure upon the free end of said slower reacting arm urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arm in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of said contact elements thereby suddenly opening said switch, said spring also following, urging and contacting said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position thereby suddenly closing said switch.

9.. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member one of said arms being so formed as to react to temperature changes at a slower rate than the other and each of said arms being anchored at one of its ends, free at the other of its ends, and so formed that in the absence of a restraining force the free end of at least one of said arms would normally tend to move away from the free end'of the other; a contact element positioned on the slower reacting of said arms near the free end thereof; a slotted contact element positioned on the other of said arms near the free end thereof for cooperative contact with the first of said contact elements; a ringer carried by said base member and positioned so as to extend into the slot oi said slotted contact element for alternately contacting the roof of said slot to limit the downward motion of said contact element and the floor of said slot to limit the upward motion of said contact element; a fulcrum bar carried by said base member; and a leaf spring convex for its entire length and having formed therein a pair of substantially parallel groves which are at right angles to the long axis of the spring loosely mounted near one of its ends on said base member, free at the other of its ends and positioned so that said grooves fall between said fuicrum bar and said free end of said spring and so that said free end of said spring exerts a pressure upon the free end of said slower reacting arm urging said end towards the free end of the other of saidarms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminishedmo permit a quick separation of said contact elements thereby suddenly opening said switch, said spring also following, urging and the switch closing direction until a certain point is reached when the force in said spring is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position thereby suddenly closing said switch.

10. A normally closed electric switch comprising a base member; two arms of thermostatic responsive material carried by said base member.

one of said arms being formed so as to react to. temperature changes at a slower rate than the other and each of said arms being anchored at one of its ends, free at the other of its ends, and so formed that in the absence of a restraining force the free end of at least one of said arms would normally tend to move away from the free end of the other; a contact element positioned on the slower reacting of said arms near the free end thereof a slotted contact element positioned on the other of said arms nearthe free end thereof for cooperative contact with lthe iirst of contacting said slower reacting arm in contact eiements; a finger carried by said e member and positioned so as to extend into 'the slot of said slotted contact element for alternately contacting the roof of said slot to limit the downward motion of said contact element and the oor of said slot to limit the upward motion oi said contact element; an electrical conducting and resistance element positioned intermediate said arms and formed so that it will permit the normal current of the circuit of which it forms a part to pass therethrough without heating appreciahly but which will heat up when an overioad current passes through said circuit; a :fulcrum bar carried by said base; and a leaf e spring convex for its entire length and having at least two substantially parallel grooves formed therein looselymounted near one of its ends on said hase member and free at the other of its ends, said spring being so positioned that said grooves fall between said fulcrum bar and said free end of said spring and so that said free end of said spring overlies and exerts a pressure upon the free end of said slower reacting arm urging it towards the free end of the other of said arms, said spring functioning so as to oppose and retard the movement of said thermostatic arms in a switch opening direction until a certain point is reached when the force in said spring opposing said arm movement is suddenly diminished to permit a quick separation of said contact elements thereby suddenly opening said switch, said spring also following,v urging and contacting said slower reacting arm in the switch closing direction until a certain point is reached when the force in said spring is suddenly increased to a point where it overcomes the resistance of said arm and forces said arm to move quickly to its switch closing position thereby suddenly closing said switch.

HEINRICH WEIRICH. 

